We have been examining the role of different stimulus attributes in the development of filial and social attachment in the squirrel monkey. The relative importance of olfactory and visual cues has been investigated in the most detail primarily by measuring preferences of infants for natural and artificial mothers under different exposure conditions. The results from various experiments have generally indicated that infants younger than four months are more responsive to odors than they are to static visual cues, and that natural odors are more potent than synthetic odors in eliciting a preference. Moreover, we have found that the alteration of natural odors associated with the mother appears to interfere with the infant's attachment to her. The effect of prolonged exposure to a specific visual property (color) on the establishment of social affiliations is also being examined by outfitting both surrogate- and mother-reared juveniles with colored jackets and housing them together in small groups containing animals with jacekts of the same color. In the case of surrogate-reared animals, the jacket color corresponds to the color of the surrogate on which they were reared for the first 6 months of life. We plan to measure preferences over a period of time for cagemates and strangers in jackets of the same and different color from those worn in the living environment, and expect that such data will provide information on the relative efficacy of different perceptual experiences following weaning, and different rearing conditions prior to weaning in the formation of social relationships.